JP6089581B2 - Porous polyolefin film, laminated porous film, and electricity storage device - Google Patents

Description

  The present invention relates to a porous polyolefin film, a laminated porous film, and an electricity storage device.

  Porous polypropylene films are being considered for use in a wide range of applications, including separators for batteries and electrolytic capacitors, various separation membranes, clothing, moisture-permeable waterproof membranes for medical applications, reflectors for flat panel displays, and thermal transfer recording sheets. Yes. Among these, a porous film is suitable as a separator for lithium ion batteries widely used in mobile devices such as notebook personal computers, mobile phones, and digital cameras. In particular, in recent years, lithium-ion batteries have been used in electric vehicles and hybrid vehicles, and as the output of batteries increases and the capacity increases, studies on coating porous films with inorganic particle layers and heat-resistant resin layers are actively conducted. (For example, refer to Patent Documents 1 and 2). Further, since the size of the battery is increased and the area to be used is increased, cost reduction is also strongly desired.

  Various proposals have been made as a method for making a polypropylene film porous. Among them, a β-crystal method is mentioned as a dry method and a method capable of forming a film with high productivity by biaxial stretching. The β crystal method is a method in which voids are formed in a film by utilizing the crystal density difference and crystal transition between α type crystal (α crystal) and β type crystal (β crystal), which are polymorphs of polypropylene. Many proposals have been made (for example, see Patent Documents 3 to 5). Furthermore, many proposals have been made on a method of coating a functional layer such as a heat-resistant layer on the surface of a porous polypropylene film by the β crystal method (see, for example, Patent Documents 6 to 14). However, a porous polypropylene film by the β crystal method is formed by impregnating an organic solvent into the film in a series of processes of transporting the film and applying and drying when coating an organic solvent-based coating material such as acetone by a roll-to-roll method. Since there is a case where wrinkles are generated at the time of conveyance due to dimensional change of the film or friction between the film and the metal roll and the flatness is deteriorated, as described in Patent Documents 6 to 14, the coating agent for coating is aqueous. However, it has been difficult to improve productivity using an organic solvent system having a high drying rate.

JP 2007-273443 A JP 2006-164873 A JP-A 63-199742 JP-A-6-100720 Japanese Patent Laid-Open No. 9-255804 JP 2009-19118 A JP 2009-114434 A JP 2009-226746 A JP 2009-227819 A JP 2010-65088 A JP 2010-219037 A JP 2011-110704 A JP 2011-126275 A International Publication No. 2010-8003 Pamphlet

  An object of the present invention is to solve the above-described problems. In other words, in the process of applying a functional layer such as a heat-resistant layer whose productivity has been improved using an organic solvent having a high drying rate, it is excellent in flatness by suppressing generation of wrinkles in the conveyed film, and is suitable as a separator for an electricity storage device. It is providing the porous polyolefin film which can be used for.

  The above-described problems are that the coefficient of friction μk with the metal in the film longitudinal direction is 1.2 or less, and the dimensional change of expansion or contraction in the film width direction in a state where the film is immersed in acetone is 0.3% or less. Achievable with porous polyolefin films.

  The porous polyolefin film of the present invention has improved wrinkle generation and deterioration of flatness in the film conveyed in the process of applying a functional layer such as a heat-resistant layer whose productivity is improved by using an organic solvent having a high drying speed. Therefore, it can be suitably used as a separator for an electricity storage device.

The porous polyolefin film of the present invention has a coefficient of friction μk with a metal in the film longitudinal direction of 1.2 or less, and a dimensional change in expansion or contraction in the film width direction in a state where the film is immersed in acetone is 0.3. % Ri der less, Ru porous polyolefin film der β crystal forming ability is 40% or more of the film.

  Here, in the present application, a direction parallel to the film forming direction is referred to as a film forming direction or a longitudinal direction or MD, and a direction orthogonal to the film forming direction in the film plane is referred to as a width direction, a lateral direction or TD. Called. When the friction coefficient μk with the metal in the longitudinal direction of the film is greater than 1.2, in the process of applying a functional layer such as a heat-resistant layer while transporting the film, the friction with the metal roll increases and the film does not slip on the metal roll. Wrinkles may occur in the longitudinal direction of the film due to the conveyance tension. The friction coefficient μk between the film and the metal is preferably 1.1 or less, more preferably 1.0 or less, and still more preferably 0.9 or less. The lower limit of the friction coefficient μk is not particularly limited, but is 0.1.

  The porous polyolefin film of the present invention is coated with a functional layer such as a heat-resistant layer while transporting the film when the dimensional change of expansion or contraction in the film width direction in a state where the film is immersed in acetone exceeds 0.3%. In the transporting process for drying the functional layer binder, wrinkles may occur in the longitudinal direction of the film. The dimensional change of expansion or contraction in the film width direction when the film is immersed in acetone is preferably 0.2% or less, and more preferably 0.1% or less. As described above, the rate of change of shrinkage and expansion is preferably as small as possible, and the functional layer such as a heat-resistant layer whose productivity has been improved by using an organic solvent having a high drying speed is applied when the expansion and contraction become the contraction side. In a process, it is preferable from a viewpoint of suppressing the wrinkle generation | occurrence | production of the film conveyed. This is because when the film comes into contact with the metal roll for transportation in the coating process, if the expansion behavior is large, the film cannot be deformed in the width direction due to friction between the metal roll and the film. It is thought that it tends to bend and form wrinkles. Here, in the coating process of a functional layer such as a heat-resistant layer whose productivity is improved by using an organic solvent having a high drying speed, the above-described friction coefficient μk and the film are used from the viewpoint of suppressing wrinkle generation of the conveyed film. In order to set the dimensional change of expansion or contraction in the width direction within the range defined by the present invention, it is possible to control the stretching, heat treatment, and relaxation conditions during film formation, which will be described later, within the ranges described later.

  The porous polyolefin film of the present invention has pores that penetrate through both surfaces of the film and have air permeability (hereinafter referred to as through-holes), and contains a polyolefin resin as a main component. “Main component” means that the proportion of a specific component in all components is 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass. This means that the amount is 100% by mass. As a method for obtaining the porous film having the through-holes, as long as the above characteristics are satisfied, the production method and material are not particularly limited, and various methods can be adopted, but the main component material is polypropylene. When used, it is preferable because the material cost can be reduced and the separator can be manufactured at a low price. As a production method, it is preferable to use the β crystal method described later, because the film can be formed with high productivity by biaxial stretching.

  Hereinafter, preferred embodiments of the porous polyolefin film of the present invention will be described by taking the β crystal method as an example.

  The porous polyolefin film of the present invention is preferably composed mainly of polypropylene having a β crystal forming ability of 40% or more. The “main component” means that the proportion of a specific component in all components is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and most preferably 95% by mass or more. It means that there is.

  The β crystal method is a method in which a β crystal formed in a cast sheet is used as fibrils oriented in the film forming direction by longitudinal stretching, and a porous polypropylene film is obtained by forming a network while cleaving the fibrils by transverse stretching. Is the method. The cast sheet refers to an unstretched sheet obtained by molding a molten polyolefin resin into a sheet shape on a cast drum.

  In order to form through-holes in the film using the β crystal method, it is preferable that the β polyolefin forming ability of the porous polyolefin film of the present invention is 40% or more. If the β-crystal forming ability is less than 40%, the amount of β-crystals is small at the time of film production, so the number of voids formed in the film is reduced by utilizing the transition to α-crystal, and as a result, only a film with low permeability is obtained. It may not be possible. On the other hand, in order to make the β crystal forming ability exceed 90%, it is necessary to add a large amount of a β crystal nucleating agent described later, or to make the stereoregularity of the polypropylene resin to be used extremely high. Industrial practical value is low, such as a decrease in stability. Industrially, β-crystal forming ability is preferably 60 to 90%, particularly preferably 65 to 85%.

  In order to control the β crystal formation ability to 40 to 90%, a polypropylene resin having a high isotactic index is used, or a β crystal is selectively added by adding it to a polypropylene resin called a β crystal nucleating agent. The crystallization nucleating agent to be formed is preferably used as an additive.

  Examples of the β crystal nucleating agent include alkali or alkaline earth metal salts of carboxylic acids such as calcium 1,2-hydroxystearate and magnesium succinate, and N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide. Amide compounds, tetraoxaspiro compounds such as 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, benzenesulfonic acid Preferable examples include aromatic sulfonic acid compounds such as sodium and sodium naphthalene sulfonate, imide carboxylic acid derivatives, phthalocyanine pigments, and quinacridone pigments. Particularly, amides disclosed in JP-A-5-310665 Compounds can be preferably usedThe content of the β crystal nucleating agent is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.3% by mass, based on the entire polypropylene composition. . If it is less than 0.05% by mass, formation of β crystals becomes insufficient, and the air permeability of the porous polypropylene film may be lowered. When it exceeds 0.5% by mass, coarse voids are formed, the functional layer such as the heat-resistant layer is applied while the film is being conveyed, and the dimensional change of the film increases before and after the functional layer binder is dried. This may cause wrinkles in the film longitudinal direction of the process.

  For the polypropylene resin used in the present invention, it is preferable to use an isotactic polypropylene resin having a melt flow rate (hereinafter referred to as MFR) of 2 to 30 g / 10 min from the viewpoint of extrusion moldability and uniform formation of pores. . Here, MFR is an index indicating the melt viscosity of a resin defined in JIS K 7210 (1995), and is a physical property value indicating the characteristics of a polyolefin resin. In the present invention, it refers to a value measured at 230 ° C. and 2.16 kg. In the present invention, the isotactic index of the polypropylene resin is preferably in the range of 90 to 99.9%. More preferably, it is 95 to 99%. When the isotactic index is less than 90%, the crystallinity of the resin is lowered, and the film forming property may be deteriorated or the strength of the film may be insufficient.

  As a polypropylene composition for forming the porous polyolefin film of the present invention, it is possible to use homopolypropylene as well as to co-polymerize propylene with a monomer other than propylene as long as the object of the present invention is not impaired. A polymerized random copolymer or block copolymer may be used, or the copolymer may be blended with polypropylene. Examples of the monomer constituting such a copolymer component or blend include, for example, ethylene, 1-butene, 1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 5-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-heptene, 1-nonene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5- Examples include, but are not limited to, methyl-2-norbornene, acrylic acid, and derivatives thereof. In a laminated film obtained by using a plurality of extruders or by a laminating method, the main component of at least one layer is preferably a polypropylene resin, and the main component of the entire laminated film is more preferably a polypropylene resin. .

  The polypropylene composition for forming the porous polyolefin film of the present invention includes an antioxidant, a heat stabilizer, an antistatic agent, a lubricant composed of inorganic or organic particles, and further an anti-blocking agent, as long as the effects of the present invention are not impaired. Various additives such as an agent, a filler and an incompatible polymer may be contained. In particular, it is preferable to add an antioxidant for the purpose of suppressing the oxidative deterioration due to the thermal history of the polypropylene resin, but the amount of the antioxidant added is 2 parts by mass or less with respect to 100 parts by mass of the polypropylene composition. The amount is preferably 1 part by mass or less, more preferably 0.5 part by mass or less.

  The polypropylene composition for forming the porous polyolefin film of the present invention may contain a pore-forming aid composed of inorganic or organic particles as long as the effects of the present invention are not impaired. The content is preferably 5 parts by mass or less with respect to 100 parts by mass of the polypropylene composition, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less. When the amount exceeds 5 parts by mass, when used as a separator, the dropped particles may deteriorate battery performance, increase raw material costs, and decrease productivity.

  In the porous polyolefin film of the present invention, the relationship between the Young's modulus fMD in the film longitudinal direction and the Young's modulus fTD in the width direction preferably satisfies the following formula.

0.8 <fMD / fTD <2
When fMD / fTD, which is the relationship between the Young's modulus fMD in the longitudinal direction of the film and the Young's modulus fTD in the width direction, is 0.8 or less, the Young's modulus in the width direction is substantially high and the TD orientation is obtained. Wrinkles of transported film during the coating process of functional layers such as heat-resistant layers, which have a large dimensional change in the film width direction when the film is immersed in the film and the productivity is improved using an organic solvent with a high drying speed Is likely to occur. On the other hand, when fMD / fTD is 2 or more, the Young's modulus in the substantial longitudinal direction is extremely high, and it is necessary to increase the stretching ratio in the longitudinal direction in the stretching process during film production. May decrease. From the above viewpoint, the relationship between the Young's modulus fMD in the longitudinal direction of the film and the Young's modulus fTD in the width direction is preferably balanced or has a slightly high Young's modulus, preferably 0.9 <fMD / fTD <1.8. 0.0 <fMD / fTD <1.6 is more preferable.

  The Young's modulus fMD in the longitudinal direction of the porous polyolefin film of the present invention is preferably 500 MPa or more. If the Young's modulus fMD in the longitudinal direction is less than 500 MPa, the rigidity of the film itself is insufficient, and the film may be deformed and wrinkled at the transport tension controlled by unwinding / winding in the coating and transporting process. is there. In order to increase fMD, it is necessary to increase the draw ratio in the longitudinal direction in the drawing process during film production, and production efficiency may be reduced such as tearing and tearing in the longitudinal direction, and the balance of fMD / fTD is also in a preferred range. From the viewpoint, the Young's modulus fMD in the longitudinal direction is 500 MPa or more, more preferably 550 MPa or more, and further preferably 600 MPa or more and 1,200 MPa or less. In the present invention, the upper limit of fMD is not particularly limited, but is substantially 2,000 MPa.

  In the porous polyolefin film of the present invention, the relationship between the 5% elongation stress (f5-MD) in the film longitudinal direction and the 5% elongation stress (f5-TD) in the width direction obtained by a tensile test satisfies the following formula: preferable.

0.7 <(f5-MD) / (f5-TD) <1.8
(F5-MD) / (f5-TD), which is the relationship between the 5% elongation stress (f5-MD) in the longitudinal direction of the film and the 5% elongation stress (f5-TD) in the width direction obtained in the tensile test, is 0. .7 or less, the f5 value in the width direction is substantially high and TD-oriented, and the dimensional change in the film width direction is large when the film is immersed in acetone, and the organic solvent has a high drying rate. In the process of applying a functional layer such as a heat-resistant layer whose productivity has been improved by using wrinkles, wrinkles of the conveyed film are likely to occur. On the other hand, when (f5-MD) / (f5-TD) is 1.8 or more, the f5 value in the substantial longitudinal direction is extremely high, and it is necessary to increase the stretching ratio in the longitudinal direction in the stretching process during film production. In some cases, production efficiency may decrease due to vertical tearing and tearing. From the above viewpoint, the relationship between the 5% elongation stress (f5-MD) in the longitudinal direction of the film and the 5% elongation stress (f5-TD) in the width direction obtained by the tensile test is balanced or the MD has a slightly high f5 value. The state is preferable, 0.8 <(f5-MD) / (f5-TD) <1.6 is preferable, and 0.9 <(f5-MD) / (f5-TD) <1.4 is more preferable.

  Further, the stress at 5% elongation (f5-MD) in the longitudinal direction of the film obtained by a tensile test of the porous polyolefin film of the present invention is preferably 20 MPa or more. When (f5-MD) is less than 20 MPa, the rigidity of the film itself is insufficient, and the film may be deformed and wrinkled in the transport tension controlled by unwinding / winding in the coating and transporting process. . When increasing (f5-MD), it is necessary to increase the draw ratio in the longitudinal direction in the stretching process during film production, and the production efficiency may decrease, such as tearing and tearing, and (f5-MD) / From the viewpoint of setting the balance of (f5-TD) as a preferable range, (f5-MD) is 20 MPa or more, more preferably 23 MPa or more, and further preferably 25 MPa or more. In the present invention, the upper limit of fMD is not particularly limited, but is substantially 50 MPa.

  The porous polyolefin film of the present invention preferably has a heat shrinkage rate of 3% or less in the film width direction after treatment at 120 ° C. for 1 hour. When the heat shrinkage rate exceeds 3%, when used as a power storage device separator, the heat shrinkage may easily cause shrinkage and cause a short circuit. The smaller the heat shrinkage rate, the better. However, the lower limit is substantially about 0.01%, and the heat shrinkage rate in the width direction after treatment for 1 hour at 120 ° C. is 0 as a separator for an electricity storage device. It is preferably 0.01% or more and 3% or less, more preferably 0.01% or more and 2% or less, and still more preferably 0.01% or more and 1% or less. In order to make the heat shrinkage rate within a preferable range, it is possible to appropriately adjust the stretching, heat treatment, and relaxation rate described later.

  The porous polyolefin film of the present invention preferably has a porosity of 35 to 85%. When the porosity is less than 35%, the electrical resistance may increase particularly when used as a separator for a high-power battery. On the other hand, when the porosity exceeds 85%, the dimensional change of expansion or contraction in the film width direction in a state where the film is immersed in acetone may increase. In the step of applying a functional layer such as a heat-resistant layer whose productivity has been improved by using an organic solvent having a high drying speed, the porosity of the film is 38 to 75% from the viewpoint of suppressing wrinkle generation of the conveyed film. It is more preferable if it is 40 to 70%. The porosity can be controlled by setting the temperature of the cast drum, which will be described later, the stretching ratio and temperature in the longitudinal direction, the temperature and time in the heat treatment step, and the relaxation rate in the relaxation zone to be in the range described later.

  The porous polyolefin film of the present invention preferably has an air resistance of 50 to 1,000 seconds / 100 ml, more preferably 70 to 800 seconds / 100 ml, more preferably 90 to 600 seconds / 100 ml, and most preferably 100 to 500. Sec / 100 ml. When the air resistance exceeds 1,000 seconds / 100 ml, the output characteristics may be deteriorated when used for a separator. From the viewpoint of output characteristics, the air permeability resistance is preferably as low as possible. However, if it is less than 50 seconds / 100 ml, the mechanical strength of the film is lowered, the handling property is lowered, and the electrical characteristics such as the cycle characteristics when used for a separator. May decrease. When the air resistance is controlled by the β crystal method, it can be controlled by setting the conditions during stretching and the conditions of heat treatment / relaxation treatment described later within the ranges described later.

  In addition, when carrying out the control of the air resistance according to the operating conditions of the film forming machine, the porosity of the porous polyolefin film increases when trying to reduce the air resistance, and the film width in the state where the film is immersed in acetone In some cases, the dimensional change in the direction of expansion or contraction is large. Therefore, in the present invention, by setting the conditions after the heat treatment conditions after transverse stretching to specific conditions as described later, the air permeability resistance is low and the film width direction expansion in the state where the film is immersed in acetone or A porous polyolefin film having a small dimensional change in shrinkage could be obtained.

  The porous polyolefin film of the present invention preferably has a film thickness of 5 to 50 μm. If the thickness is less than 5 μm, the film may break at the time of use, and if it exceeds 50 μm, the volume ratio of the porous polyolefin film in the electricity storage device becomes too high, and it may not be possible to obtain a high energy density. . From this viewpoint, the film thickness is more preferably 10 to 30 μm, and still more preferably 12 to 25 μm.

  The porous polyolefin film of the present invention may have a laminated structure for the purpose of imparting various effects as long as the effects of the present invention are not impaired. The number of stacked layers may be a two-layer stack, a three-layer stack, or a larger number of stacks. As a lamination method, either a feed block method by co-extrusion or a multi-manifold method, or a method of laminating porous films by lamination may be used. In the case of a laminated structure, it is preferable that the resin constituting the surface layer does not contain a polyethylene resin or an ethylene copolymer resin. When an ethylene component is present in the surface layer, the oxidation resistance may decrease when used as a battery separator.

  Below, the manufacturing method of the porous polyolefin film of this invention is demonstrated based on a specific example. In addition, the manufacturing method of the film of this invention is not limited to this.

  99.5 parts by mass of a commercially available homopolypropylene resin having a MFR of 8 g / 10 min as the polypropylene resin, 0.3 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxyamide as the β crystal nucleating agent, and 0 antioxidant The raw material is fed from the weighing hopper to the twin screw extruder so that 2 parts by mass are mixed at this ratio, melt kneaded, discharged from the die in the form of strands, cooled and solidified in a 25 ° C. water bath, and chips A polypropylene raw material (a) is prepared by cutting into a shape. At this time, the melting temperature is preferably 270 to 300 ° C.

  Next, the polypropylene raw material (a) is supplied to a uniaxial melt extruder, and melt extrusion is performed at 200 to 230 ° C. Next, after removing foreign substances, modified polymers, and the like with a filter installed in the middle, they are discharged from a T-die onto a cast drum to obtain an unstretched sheet. Here, the cast drum preferably has a surface temperature of 105 to 130 ° C. from the viewpoint of controlling the β crystal fraction of the cast film to be high. At this time, particularly, the forming of the end portion of the sheet affects the subsequent stretchability, and therefore it is preferable that the end portion is sprayed with spot air to be in close contact with the drum. Further, air may be blown over the entire surface using an air knife as necessary from the state in which the entire sheet is in close contact with the drum.

  Next, the obtained cast film is biaxially oriented to form pores in the film. As a biaxial orientation method, the film is stretched in the longitudinal direction of the film and then stretched in the width direction, or the sequential biaxial stretching method in which the film is stretched in the width direction and then stretched in the longitudinal direction. The simultaneous biaxial stretching method can be used, but it is preferable to adopt the sequential biaxial stretching method from the viewpoint that it is easy to obtain a film having a good balance between air permeability and film mechanical properties, and in particular, stretching in the longitudinal direction. Then, it is preferable to extend in the width direction.

  As specific stretching conditions, first, the temperature at which the cast film is stretched in the longitudinal direction is controlled. As a temperature control method, a method using a temperature-controlled rotating roll, a method using a hot air oven, or the like can be adopted. The stretching temperature in the longitudinal direction is preferably 90 to 140 ° C. If it is less than 90 degreeC, a film may fracture | rupture. If it exceeds 140 ° C., the pore structure may become non-uniform or the air permeability may be reduced. A higher longitudinal stretching temperature tends to have a higher Young's modulus fMD in the longitudinal direction. From this viewpoint, it is more preferably 110 to 135 ° C, particularly preferably 120 to 130 ° C. The draw ratio is preferably 3 to 6.5 times. The Young's modulus fMD in the longitudinal direction is improved as the stretching ratio is increased. However, if the stretching ratio exceeds 6.5 times, the film may be easily broken in the next transverse stretching step. The draw ratio is more preferably 4.5 to 6 times.

  Subsequently, the end of the film after longitudinal stretching is gripped with a clip, and lateral stretching is performed while maintaining the tension in the longitudinal direction. The transverse stretching temperature is preferably 130 to 155 ° C. If it is less than 130 degreeC, a film may fracture | rupture, and if it exceeds 155 degreeC, air permeability may fall. More preferably, it is 145-155 degreeC. The draw ratio in the width direction is preferably 2 to 12 times. If it is less than 2 times, the air permeability may decrease or the planarity in the width direction may decrease. If it exceeds 12 times, the film may break. If the draw ratio in the width direction is too high, the Young's modulus fMD in the longitudinal direction may be lowered. Therefore, it is preferably 3 to 10 times, more preferably 4 to 9 times. The transverse stretching speed at this time is preferably 500 to 6,000% / min, more preferably 1,000 to 5,000% / min. The area magnification (longitudinal stretching magnification × lateral stretching magnification) is preferably 30 to 60 times.

  Subsequent to the transverse stretching, a heat treatment step is performed with the width after the transverse stretching. Here, the heat treatment step is a heat setting zone (hereinafter referred to as HS1 zone) in which heat treatment is performed with the width after transverse stretching, and the heat treatment is performed while the film is relaxed in the width direction by narrowing the clip width in the width direction after transverse stretching. There are three zones: a relaxation zone (hereinafter referred to as Rx zone) to be performed, and a heat setting zone (hereinafter referred to as HS2 zone) in which heat treatment is performed with the width after relaxation. In the present invention, after the HS2 zone, stretching with a small stretching ratio in the width direction (hereinafter sometimes referred to as micro-stretching) is a state in which the film is immersed in acetone and air permeability is exhibited, the mechanical properties are balanced. Is preferable from the viewpoint of reducing the dimensional change of expansion or contraction in the film width direction.

  The temperature of the HS1 zone is preferably 140 to 165 ° C. When the temperature is lower than 140 ° C., the dimensional change of expansion or contraction in the film width direction in a state where the film is immersed in acetone may increase. If the temperature exceeds 165 ° C, the orientation of the film is too relaxed, the relaxation rate cannot be increased in the subsequent Rx zone, and it is difficult to achieve both air permeability and mechanical strength. Resistance may increase. 150 to 165 [deg.] C. is more preferable from the viewpoint of air permeability expression, balancing of mechanical properties, and reduction in dimensional change of expansion or contraction in the film width direction in a state where the film is immersed in acetone.

  The heat treatment time in the HS1 zone is preferably 0.1 seconds or longer and 10 seconds or shorter from the viewpoint of achieving both a heat shrinkage ratio in the width direction and productivity.

  In the present invention, the relaxation rate in the Rx zone is preferably 13 to 35%. If the relaxation rate is less than 13%, the thermal contraction rate in the width direction may increase. If it exceeds 35%, the air permeability may decrease, or the thickness unevenness or flatness in the width direction may decrease. From the viewpoint of reducing the dimensional change of expansion or contraction in the film width direction in a state where the mechanical properties are balanced and the film is immersed in acetone, it is more preferably 15 to 25%.

  The temperature of the Rx zone is preferably 155 to 170 ° C. When the temperature of the Rx zone is lower than 155 ° C., the shrinkage stress for relaxation is lowered, and the above-described high relaxation rate may not be achieved or the thermal shrinkage rate in the width direction may be increased. If the temperature exceeds 170 ° C., the polymer around the pores may melt at a high temperature and the air permeability may be lowered. From the viewpoint of improving air permeability and reducing the heat shrinkage rate, it is more preferably 160 to 165 ° C.

  The relaxation rate in the Rx zone is preferably 100 to 1,000% / min. When the relaxation rate is less than 100% / min, it is necessary to slow down the film forming rate or lengthen the tenter length, which may be inferior in productivity. If it exceeds 1,000% / min, the speed at which the film shrinks will be slower than the speed at which the rail width of the tenter shrinks, and the film may flutter within the tenter and tear, or the thermal contraction rate in the width direction may increase. . The relaxation rate is more preferably 150 to 500% / min.

  The temperature of the HS2 zone is preferably 155 to 165 ° C. If the temperature is lower than 155 ° C., the tension of the film after thermal relaxation becomes insufficient, resulting in uneven physical properties and flatness in the width direction, and may increase the heat shrinkage rate in the width direction. If it is less than 155 ° C., the Young's modulus fMD in the longitudinal direction may be insufficient. On the other hand, if the temperature exceeds 165 ° C., the polymer around the pores may melt at a high temperature and the air permeability may decrease. From the viewpoint of reducing the dimensional change of expansion or contraction in the film width direction in the state where air permeability is exhibited, the mechanical properties are balanced, and the film is immersed in acetone, the temperature of the HS2 zone is more preferably 160 to 165 ° C. preferable. The heat treatment time in the HS2 zone is preferably 0.1 seconds or more and 10 seconds or less from the viewpoints of mechanical strength, physical property unevenness in the width direction, and compatibility between flatness and productivity.

  In the present invention, dimensional change of expansion or contraction in the film width direction in a state where the film is immersed in acetone by performing micro stretching of 1.01 to 1.1 times in the width direction in the slow cooling atmosphere after the HS2 zone. Is also preferable from the viewpoint of reducing the size and the contraction side. In each zone HS1, Rx, HS2 immediately before, the residual strain due to stretching is sufficiently released, so that the dimensional change in the film width direction when the film is immersed in acetone tends to become large on the expansion side. It is considered that the TD orientation can be changed while maintaining the orientation, and as a result, the dimensional change that has become larger on the expansion side can be reduced and further on the contraction side. The fine stretching speed is preferably 100 to 1,000% / min. When the fine stretching speed is less than 100% / min, it is necessary to slow down the film forming speed or increase the tenter length, which may be inferior in productivity. If it exceeds 1,000% / min, the speed at which the film is finely stretched is slower than the speed at which the rail width of the tenter is widened, and the ten film may be torn, resulting in uneven physical properties in the width direction and a decrease in flatness. The fine stretching speed is more preferably 150 to 500% / min. If the fine stretching exceeds 1.1 times, the film may be broken during film formation.

  Next, the film after fine stretching is made into a product by removing the ears gripped by the clips of the transverse stretching machine.

  Thereafter, a coated layer may be provided on at least one side to form a laminated porous film. Since the porous polyolefin film of the present invention is excellent in resistance to organic solvents, it is possible to maintain high air permeability even when coating is performed using an organic solvent. Various methods can be used as the coating method. For example, at least one organic solvent selected from acetone, ethanol, tetrahydrofuran, N-methyl-2-pyrrolidone and the like is used as a solvent, and heat-resistant resin and inorganic particles are used. Add additives such as binders accordingly, prepare coatings, apply to at least one side of the porous polyolefin film of the present invention using a die coating method or gravure coating method, and dry the solvent using a drying oven By doing so, a laminated porous film can be obtained.

  Since the porous polyolefin film and laminated porous film of the present invention are excellent in strength and heat resistance, they are separators for batteries and electrolytic capacitors, various separation membranes, clothing, moisture-permeable waterproof membranes for medical use, and reflectors for flat panel displays. Can be used in a wide variety of applications such as thermal transfer recording sheets and thermal transfer recording sheets, and is suitable as a separator for power storage devices that are widely used in mobile devices such as notebook personal computers, mobile phones, and digital cameras.

  Here, examples of the electricity storage device include a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, and an electric double layer capacitor such as a lithium ion capacitor. Since such an electricity storage device can be repeatedly used by charging and discharging, it can be used as a power supply device for industrial devices, household equipment, electric vehicles, hybrid electric vehicles, and the like. In particular, an electricity storage device using a separator using the porous polyolefin film of the present invention is suitable as a porous film for a substrate for coating a surface layer with a functional layer such as a heat-resistant layer. Furthermore, since the laminated porous film provided with a functional layer such as a heat-resistant layer on the porous polyolefin film of the present invention is excellent in output characteristics and safety, it can be suitably used for a non-aqueous electrolyte secondary battery for an electric vehicle. it can.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) Friction coefficient with metal μk
The friction coefficient μk in the film longitudinal direction was measured using a tape running tester under the following conditions.

Measuring device: Tape running tester TBT-300 type, manufactured by Yokohama System Laboratory Co., Ltd. Sample dimensions: 10 mm in the width direction, 300 mm in the longitudinal direction (measurement length: 100 mm)
Measurement environment: Temperature 23.5 ° C, humidity 65% RH
Guide roll: SUS27 (6mmφ, surface roughness 0.2S)
Winding angle: 90 °
Travel speed: 3.3cm / s
Initial load: 30g
Repeated running times: 10 times The film edge is attached to a tape running tester with an adhesive tape, and is placed along a guide roll. An initial load weight was hung on the end of the film opposite to the device attaching portion, and measurement was performed.

  The friction coefficient μk was calculated from the entry side tension T1 and the exit side tension T2 using the following equation.

Friction coefficient μk = (2 / π) × ln (T1 / T2)
The first friction coefficient was calculated as μk.

(2) Dimensional change during impregnation with acetone A sample of a porous polyolefin film was cut into a rectangle of longitudinal direction × width direction: 150 mm × 200 mm, and the distance of the long side of the sample was measured with a digital caliper. It was set as the dimension (L ₀ ). Next, the sample is put in a polyethylene bag Unipack I-4 (280 × 2,000 × 0.04 mm) with a chuck manufactured by Nippon Production Co., Ltd., 20 ml of acetone is put in, the chuck of the polyethylene bag is closed, and the sample is put in acetone for 5 minutes. After soaking, the distance of the long side where the initial dimension was measured in the state of being put in the polyethylene bag was measured with a digital caliper, and the dimension when immersed in acetone in the width direction (L ₁ ) was obtained. The dimensional change during acetone impregnation was calculated from the following equation. When the value is negative, it is contracted, and when it is positive, it is expanded.

Dimensional change during acetone impregnation = {(L ₁ −L ₀ ) / L ₀ } × 100 (%)
(3) Young's modulus in the longitudinal direction (fMD) and Young's modulus in the width direction (fTD)
The measurement was performed according to the measurement method defined in JIS K7127 (1999). The porous polyolefin film was cut into rectangles each having a length of 150 mm and a width of 10 mm in the longitudinal direction and the width direction as samples. In an atmosphere of 23 ° C. and 65% RH, using a tensile tester (Orientec Tensilon UCT-100), the distance between the initial chucks was 50 mm, the tensile speed was 300 mm / min, and the film was pulled in the longitudinal and width directions. A test was conducted. The measurement was performed 5 times for each sample, and the average value was obtained.

  The film thickness was measured as follows. A contact type dial gauge thickness gauge (JIS B-7503 (1997), UPAIGHT DIAL GAUGE made by PEACOCK (0. 001 × 2 mm), No. 25, probe 10 mmφ flat type, 50 gf load), the thickness was measured, and the average value was taken as the thickness of the porous polyolefin film.

(4) 5% elongation stress in the longitudinal direction (f5-MD) and 5% elongation stress in the width direction (f5-TD)
A tensile test was performed in the longitudinal direction and the width direction of the film in the same manner as in the above (3). The measurement was performed five times for each sample, and the stress at the time when the tensile elongation was 5% was read from the stress-strain curve, and the average value was obtained.

(5) β crystal forming ability 5 mg of a porous polyolefin film was sampled in an aluminum pan and measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). First, the temperature is raised from room temperature to 260 ° C. at a rate of 10 ° C./minute (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 20 ° C. at a rate of 10 ° C./minute. After holding for 5 minutes, the melting peak observed when the temperature is raised again at 10 ° C./min (second run) is the melting peak of the β crystal at 145 ° C. to 157 ° C., 158 ° C. The melting at which the peak is observed is defined as the melting peak of the α crystal, and the melting heat amount of the α crystal is obtained from the baseline and the area of the region surrounded by the peak drawn from the flat portion on the high temperature side. Is the ΔHα, and the heat of fusion of the β crystal is ΔHβ, the value calculated by the following formula is the β crystal forming ability. The heat of fusion was calibrated using indium.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, the β crystal fraction in the state of the sample can be calculated by calculating the abundance ratio of the β crystal in the same manner from the melting peak observed in the first run.

(6) Air permeability resistance A square having a size of 100 mm × 100 mm was cut out from the porous polyolefin film and used as a sample. Using a JIS P 8117 (1998) B-type Gurley tester, the permeation time of 100 ml of air was measured at 23 ° C. and a relative humidity of 65%. The measurement was performed three times with the sample changed, and the average value of the permeation time was defined as the air permeability of the film. In addition, it can confirm that the through-hole is formed in the film that this air permeability value is a finite value.

(7) Thermal shrinkage rate at 120 ° C. for 1 hour (width direction)
In the width direction of the film, five samples having a width of 10 mm and a length of 200 mm are cut out and marked at a position of 25 mm from both ends to give a test length of 150 mm (l ₀ ). Next, it is hung in an oven kept at 120 ° C. with a load of 3 g, taken out after heating for 1 hour, cooled at room temperature, measured for the dimension (l ₁ ), and calculated by the following formula. The average value was defined as the heat shrinkage rate.

Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%)
(8) Degree of generation of wrinkles during conveyance A porous polyolefin film roll was slit into a width of 250 mm to obtain a film roll having a length of 100 m. A film roll is set on the unwinding machine, and transported at a transport speed of 13 m / min and a transport tension of 1.5 kg / 250 mm with two HCr metal free rolls (surface roughness Ra = 0.4 μm) interposed therebetween. Winded up. During transportation, the film is transported for 5 minutes while spray coating so that the film fully penetrates with acetone in the section from the unwinder through the first HCr metal free roll. The presence or absence of folds in the MD direction that occurred in the first section was visually observed. Of the five minutes being conveyed, the total ratio of the time when wrinkles occurred was measured and evaluated according to the following criteria. ◎ and ○ are acceptable.

◎: 0% or more and less than 5% ○: 5% or more and less than 10% ×: 10% or more (Example 1)
As the polyolefin resin, 99.5 parts by mass of Homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd. having a melting point of 165 ° C. and MFR = 7.5 g / 10 min, N, N′-dicyclohexyl-2,6- 0.3 parts by mass of naphthalene dicarboxyamide (manufactured by Shin Nippon Rika Co., Ltd., NU-100), and 0.1 parts by mass each of IRGANOX 1010 and IRGAFOS 168 by Ciba Specialty Chemicals, which are antioxidants, The raw material is supplied from the weighing hopper to the twin screw extruder so that it is mixed at 300 ° C, melted and kneaded at 300 ° C, discharged from the die into strands, cooled and solidified in a 25 ° C water bath, and cut into chips. Thus, a polypropylene composition was obtained.

  The obtained polypropylene composition was supplied to a uniaxial melt extruder, melt extruded at 220 ° C, foreign matter was removed with a 25 µm cut sintered filter, and the cast drum whose surface temperature was controlled from a T die to 125 ° C. To obtain an unstretched sheet. Next, preheating was performed using a ceramic roll heated to 124 ° C., and the film was stretched 5.5 times in the longitudinal direction of the film. Next, the film edge after longitudinal stretching was held with a clip and introduced into a transverse stretching machine, stretched 8.5 times at 149 ° C., and at a stretching speed of 1,800% / min. The heat treatment is performed at 163 ° C. in the HS1 zone while holding the width direction as it is, and then the heat treatment is performed at 163 ° C. while relaxing 20% in the width direction. Finally, the heat treatment is performed at 163 ° C. in the HS2 zone while holding the width direction. Heat treatment was performed, and a fine stretching of 1.015 times in the width direction was performed in a slow cooling atmosphere after the HS2 zone, and a 500 m roll product roll was obtained using a porous polypropylene film having a thickness of 17 μm as a core.

(Example 2)
In the production conditions shown in Table 1, a porous polypropylene film having a thickness of 17 μm was formed in the same manner as in Example 1 except that the transverse draw ratio was 6.5 times and the transverse draw ratio was 151 ° C. from the conditions of Example 1. The product roll was obtained by winding 500 m on the core.

(Example 3)
In the production conditions shown in Table 1, film formation was carried out in the same manner as in Example 1 except that the MD temperature during stretching was 120 ° C. and the zones of HS1, Rx, and HS2 were 161 ° C. as heat treatment conditions. A rolled product roll of 500 m was obtained using a porous polypropylene film having a thickness of 17 μm as a core.

Example 4
In the production conditions shown in Table 1, the longitudinal stretching ratio was 5.0, the longitudinal stretching temperature was 115 ° C., the lateral stretching ratio was 9.0 times, and the relaxation rate of the Rx zone was 17% from the conditions of Example 1. Was formed into a film in the same manner as in Example 1, and a rolled product roll was obtained by winding the core with a porous polypropylene film having a thickness of 17 μm.

(Example 5)
In the production conditions shown in Table 1, a film having a thickness of 17 μm was formed in the same manner as in Example 3 except that the fine stretching ratio in the width direction was changed to 1.050 times in the slow cooling atmosphere after the HS2 zone from the conditions in Example 3. The porous polypropylene film was used as a core to obtain a product roll of 500 m.

(Comparative Example 1)
In the production conditions shown in Table 1, from the conditions in Example 1, the longitudinal draw ratio was 5.0 times, the temperature was 120 ° C., the transverse draw ratio was 9.5 times, and the relaxation rate of the Rx zone after transverse drawing was 17%. Except for the above, a film was formed in the same manner as in Example 1, and a 500 m roll product roll was obtained using a porous polypropylene film having a thickness of 17 μm as a core.

(Comparative Example 2)
A film roll was obtained in the same manner as in Example 1 except that fine stretching was not performed 1.015 times in the width direction in the slow cooling atmosphere after the HS2 zone, and a rolled polypropylene film having a thickness of 17 μm was used as a core to obtain a product roll of 500 m. It was.

(Comparative Example 3)
In the production conditions shown in Table 1, the longitudinal stretching ratio was 5.0 times, the longitudinal stretching temperature was 120 ° C., the transverse stretching ratio was 9.5 times, the transverse stretching temperature was 148 ° C., HS1, Rx, HS2 from the conditions of Example 1. Each zone was formed in the same manner as in Example 1 except that the temperature was set at 164 ° C., and a product roll was obtained by winding a 500 m roll with a porous polypropylene film having a thickness of 17 μm as a core.

(Comparative Example 4)
In the production conditions shown in Table 1, a film having a thickness of 17 μm was formed in the same manner as in Example 1 except that the fine stretching ratio in the width direction was changed to 1.200 times in the slow cooling atmosphere after the HS2 zone from the conditions in Example 1. The porous polypropylene film was used as a core to obtain a product roll of 500 m.

  In the examples satisfying the requirements of the present invention, not only the air permeability and thermal dimensional stability are excellent, but also the coefficient of friction μk with the metal in the longitudinal direction of the film is small, and the expansion in the film width direction when the film is immersed in acetone. Or, since the dimensional change of shrinkage is small, in the process of applying a functional layer such as a heat-resistant layer whose productivity has been improved using an organic solvent with a fast drying rate, the generation of wrinkles in the conveyed film is suppressed, and the flatness It is considered that it can be suitably used as a separator for an electricity storage device. On the other hand, in the comparative example, an organic solvent having a high drying rate is used, such as a large coefficient of friction μk with the metal in the film longitudinal direction and a large dimensional change in expansion or contraction in the film width direction when the film is immersed in acetone. In the step of applying a functional layer such as a heat-resistant layer that has improved productivity, wrinkle generation of the conveyed film cannot be suppressed, the flatness is poor, and it is difficult to use as a separator for an electricity storage device.

  The porous polyolefin film of the present invention is not only excellent in air permeability and thermal dimensional stability, but also has a small coefficient of friction μk with the metal in the longitudinal direction of the film, and expansion or expansion in the film width direction in a state where the film is immersed in acetone. Since the dimensional change of shrinkage is small, in the process of applying a functional layer such as a heat-resistant layer that has improved productivity using an organic solvent with a fast drying rate, it suppresses the occurrence of wrinkles in the conveyed film and makes it flat. It is excellent and can be suitably used as a separator for an electricity storage device.

Claims (7)

Film Friction coefficient μk of the metal in the longitudinal direction is 1.2 or less state, and are dimensional change less than 0.3% of the film width direction of expansion or contraction in a state of being immersed film in acetone, the film β A porous polyolefin film having a crystal forming ability of 40% or more . The porous polyolefin film according to claim 1, wherein the heat shrinkage in the film width direction after treatment at 120 ° C for 1 hour is 3% or less. The porous polyolefin film according to claim 1 or 2, wherein a relationship between Young's modulus fMD in the longitudinal direction and Young's modulus fTD in the width direction satisfies the following formula.
0.8 <fMD / fTD <2 The porous polyolefin film in any one of Claims 1-3 whose Young's modulus fMD of a longitudinal direction is 500 Mpa or more. The porous polyolefin film according to any one of claims 1 to 4, wherein an air resistance at 23 ° C is 50 to 1,000 seconds / 100 ml. Laminated porous film comprising a coating layer provided on the porous polyolefin film of any one of claims 1-5. The electrical storage device using the porous polyolefin film in any one of Claims 1-5 , or the laminated porous film of Claim 6 as a separator.